The present invention relates to an improved rotary assembly for use in a central tire inflation system for automatically maintaining the inflation pressure of the pneumatic tires on moving vehicles such as tractor trailers. Automatic central tire inflation systems for vehicle tires are well known and the subject of several U.S. Patents, including U.S. Pat. Nos: 3,276,503; 4,387,931; 4,883,106; 5,287,906 and 5,584,949, the disclosures of which are incorporated herein by reference.
The central tire"" inflation systems employed on typical tractor trailers utilize the air compressor on the tractor as a source of pressurized air to fill a leaking tire while the trailer is in motion. The compressor directs air to the reserve air brake tank on the trailer and is set to maintain the air pressure within the tank within a range of about 100 to 125 psi, which generally corresponds to the range of typical inflation pressures in the tires used on large tractor trailers. Air from the reserve air brake tank is first directed to the braking system to maintain the air pressure in the braking system at the normal brake system level of about 70 psi. Excess air is directed from the tank through a pressure protection valve to a control box for the tire inflation system. The pressure protection valve only opens to direct the air to the control box when the air pressure in the tank exceeds 70 psi, thereby preventing air from being directed to the air inflation system which is needed for the trailer braking system. The control box contains a pressure regulator which is set to the cold tire pressure of the particular tires on the trailer so as to supply air to the tires at the desired pressure level in the event of a leak. Air is directed from the control box to the leaking tire through one of the trailer axles, which either carries an air line from the control box, or is sealed and functions as an air conduit. The pressurized air carried by the axles communicates with each pair of trailer tires mounted thereon through a rotary union assembly by which air flow is directed from a stationary air line to the valve stems on the rotating tires. Pressure responsive valves are employed between each rotary union assembly and its associated tires so that upon the occurrence of a leak in one of the tires, the resulting pressure loss will cause one of the valves to open and allow air flow from the rotary union assembly to pass therethrough to the leaking tire.
While these central tire inflation systems are well known and in widespread use, they suffer from several shortcomings. The rotary union assemblies employed in these systems have a relatively limited useful life span before the rotary seals begin to leak. The rotary seals, or rotary unions as they are frequently called, which are employed in these assemblies are generally located within the wheel lubrication compartments adjacent the ends of the axles. Accordingly, any air leakage in the rotary union seals causes an air pressure build up within the lubrication compartment which can damage the oil seals therein, and create an oil leak. If the wheel bearings loose their lubrication, they will seize up and can cause a fire. In addition to creating the potential for a dangerous fire, the positioning of the rotary union within the lubrication compartment of the wheel makes accessibility to the elements comprising the rotary union both difficult and awkward. As a result, the costs of repair and replacement are significantly increased.
The present invention provides a rotary union assembly for automatic central tire inflation systems which exhibits a substantially longer life than the rotary union assemblies heretofore in use. In addition, the assembly is configured so as to position the rotary union outside of the lubrication compartment for the vehicle wheels and thus avoids pressure build-ups within the compartment in the unlikely event of a leak in the rotary union seal. The assembly also provides ready access to the rotary union components thereof without having to enter the lubrication compartment to facilitate part replacement. As a result, the present invention provides a substantial improvement in air pressure maintenance systems for tractor trailer tires.
Other problems facing central tire inflation systems include a lack of uniformity in tractor trailer wheel hub cap configurations and off-center mountings. The former situation results in variations in the axial distance between the ends of the axle spindles and end walls of the hub caps. This distance generally determines the spacing between the air inlet of the assembly and the rotary seal therein. It would be highly desirable to provide a rotary union assembly which could readily accommodate such dimensional variations and thereby obviate the need to provide differently sized assemblies or replacement components for different hub cap configurations. The rotary union assembly should also accommodate off-center alignments of the axle spindle and hub caps without incurring additional wear on the air seals in the assembly which further shortens the life of the assembly. The rotary union assembly of the present invention achieves these objectives as well.
Briefly, the present invention is directed to a rotary union assembly for use in automatic tire inflation systems for vehicle tires and, particularly, for use in automatic inflation systems employed on tractor trailers having pressurized stationary axles. The rotary union assembly of the present invention communicates the valve stems on a pair of adjacent tires with the pressurized axle interior through the use of a stationary flexible air hose communicating at its upstream end with the axle interior through a stationary o-ring seal and at its downstream end with a rotary housing containing the rotary seal. The housing is sealably secured against the exterior surface of the end wall of the hub cap so as to be rotatable with the hub cap and tire. The o-ring seal is provided in a through flow fitting threadably secured in the extended end of the axle spindle so as to form an air tight seal about the upstream portion of the stationary air hose which allows for the length of the air hose projecting from the o-ring to the rotary housing to be readily varied by the simple insertion or retraction of line from the fitting during installation, thereby accommodating wide variations in hub cap configurations without the need for part replacement and without adversely affecting the integrity of the seal. As both the flexible air hose and the fitting through which it extends are stationary, wear is virtually eliminated at this juncture of the assembly.
The use of a flexible air hose between the axle spindle and rotary housing, allows for inadvertent off-center mountings of the rotary housing relative to the threaded fitment on the axle spindle without significantly affecting either the integrity or the life of the air seals in the assembly. Positioning the rotary housing against the exterior end surface of the hub cap locates the rotary seal formed therein outside of the lubrication compartment of the wheel and thereby prevents pressure build ups within the lubrication compartment in the event of air leakage in the rotary seal.
The rotary seal of the present invention includes an elongated stationary shaft having an air passageway extending axially therethrough. The shaft carries the downstream end of the flexible air hose and projects through and is carried by a pair of bearing members disposed in an extended portion of the rotary housing. The extended portion of the housing projects axially through the hub cap end wall such that the shaft communicates the pressurized tractor trailer axle with the interior of the rotary housing while providing a rotatable mounting of the rotary housing on the stationary shaft. A spring biased graphite element having a centrally disposed axial passageway is mounted in a fixed disposition within the housing so as to be rotatable therewith. The element is pressed against the downstream end of the elongated shaft in a flush disposition therewith to form with the shaft a rotary union by which air flow passes from the stationary flexible air hose into the rotating housing.
In the rotary housing mounted on the end wall of the hub cap, air is directed from the rotary union through two opposed channels into separate air lines which communicate with the valve stems on the pair of adjacent tires. Pressure responsive valves are provided in each of the lines to allow air flow through the appropriate line in response to a downstream pressure drop as would occur in the event of a leak in one of the tires. A normally open pressure responsive valve is also provided in each line which closes in the event of a drop in pressure upstream of the rotary union as would occur when the compressor is shut down to prevent the trailer tires from deflating. A warning light is also provided in the system for indicating to the driver the activation of the central tire inflation system.
It is the principal object of the present invention to provide an improved rotary union assembly for use in central tire inflation systems employed on tractor trailers.
It is another object of the present invention to provide a rotary assembly for use in central tire inflation systems which exhibits a substantially longer useful life than the rotary union assemblies heretofore available.
It is another object of the present invention to provide a rotary union assembly for use in a central tire inflation system for automatically maintaining the inflation pressure of the pneumatic tires on moving vehicles such as tractor trailers which reduces the possibility of a pressure build up within the lubrication compartments of the wheels.
It is a further object of the present invention to provide a rotary union assembly for a central tire inflation system which minimizes any wear in the air seals of the assembly as a result of off-center mountings between the rotary housing and air outlet in the axial spindle.
It is a still further object of the present invention to provide a rotary union assembly for use in a central tire inflation system which allows one to remove and replace the components of the rotary union exteriorly of the hub cap so as to obviate the need to remove the hub cap and risk contaminating an otherwise sealed area to effect part replacement.
It is yet another object of the present invention to provide a rotary union assembly for use in a central tire inflation system which is adaptable for use with a wide variety of differently configured wheel hub caps without the need for part replacement.
It is another object of the present invention to provide a rotary union assembly for use in a central tire inflation system which provides a high volume air flow to the tires to handle high volume air leaks and reduce the tire inflation time in the event of a flat tire.
It is still further object of the present invention to provide a rotary union assembly for use in central tire air inflation systems which is of simple construction and economical to manufacture.
These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.